Year
2004
Abstract
This report describes a technique used to measure the average neutron energy on impure plutonium samples. This measurement is done using the Epithermal Neutron Multiplicity Counter (ENMC). The measurement of neutron energy is done at the same time as the accountability or safeguards measurement. Neutron totals and coincidence measurements of plutonium have the problem that impurities present a in sample add to the observed neutron counts because of alpha particle induced source neutrons and the related multiplication. The primary signal that is needed to measure the 240Pu effective mass is the spontaneous fission rate; however, induced fissions related to the impurities increase the observed response. In most cases, the ( ,n) source neutrons have an energy distribution that is different than that for spontaneous fission. Thus, the ability to measure the neutron energy distribution helps in the identification of impure plutonium samples. A description of the ENMC detector components and discussion on the average neutron energy calibration are provided.